Low-loss drive system for a plurality of hydraulic actuators

ABSTRACT

The invention related to a drive system with at least two hydraulic actuators, which are supplied with a hydraulic fluid by means of at least one pump. The drive system comprises at least one further second pump ( 15′ ) arranged parallel to the first pump ( 15 ), wherein the pumps are bi-directionally speed-regulated, and a valve arrangement ( 59 ) with one inlet per pump ( 61.1, 61.2 ), wherein each one of the inlets is connected to a pump ( 15 ), and with a number of outlets ( 63.1, 63.1′, . . . 63.4, 63.4′ ) which are connected to the actuators ( 1.1 . . . 1.4 ), wherein the inlets ( 61 ) can be connected to the outlets ( 63 ) in a pre-determined manner.

DESCRIPTION

The invention relates to a drive system with at least two hydraulicactuators which are supplied with a hydraulic fluid by means of at leastone pump.

From the DE 40 30 950 A1 it is known to provide a hydraulicdouble-acting actuator with two pumps, wherein in each instance only oneof the two pumps is operative with regard to the movement of theactuator. Furthermore, as usual, loss-entailing regulating valves areused to control the actuator, and the pumps are driven at a largelyconstant speed, in one direction of rotation, by an internal combustionengine.

Machines with several actuators which must perform different operatingmovements in a completely or partially sequential manner, are usuallysupplied with hydraulic energy by means of a regulating valve circuit,that of one or several pumps which are driven at a constant speed. Thetechnical disadvantage of these systems is a low efficiency since, dueto the principle, the regulating valves convert hydraulic energy intothermal energy.

It is the object of the present invention to create a drive system whichhas a simple construction, outstanding regulating properties and at thesame time avoids the principle-related throttle losses of regulatingvalves and, accordingly, operates with a very good efficiency.

According to the invention a hydraulic actuator can be controlled orregulated by two bi-directional, speed-regulated pumps without anyregulating valve and, accordingly, in an extremely low-loss way infour-quadrant operation. Because the two pumps have one valve circuit,in particular in the case of sequential operations the two pumps canboth be assigned to the active actuator or, in the case of single-actionoperation, to two actuators. The valve arrangement permits in anadvantageous manner the use of only two pumps, which via the valvearrangement can be connected to the individual actuators in a low-lossmanner. It is possible, therefore, to dispense with a greater number ofpumps, which simplifies the construction and makes it more economical.The valve arrangement essentially serves to produce the low-lossconnection between the pumps and the actuators, wherein the regulatingfunctions are ensured directly by the pumps.

In an advantageous embodiment of the invention the valve arrangement hasseveral switching positions, in which in each instance one actuator inthe double-acting operating mode is connected to both pumps.

In another advantageous embodiment the valve arrangement has switchingpositions which permit the two pumps to be connected to differentactuators, so that, therefore, two actuators can be operatedsimultaneously.

Preferably, the valve arrangement has switching positions in which thetwo pumps can be connected in parallel and jointly supply one actuator.

In another advantageous embodiment the valve arrangement can be providedwith seat valves so as to fix in a leakage-free manner the actuatorswhich are not being driven at the time.

In another advantageous embodiment the valve arrangement forsingle-acting actuators can be provided with holding valves.

Preferred is an embodiment of the drive which is characterised in thatat least one of the pumps has a constant displacement volume. Such pumpsare of a particularly simple construction, resulting in an economicalrealisation which is not susceptible to problems.

Furthermore preferred is an embodiment of the drive which comprises acontrol which co-operates with the drive, is designed as a regulatingcircuit and includes at least one sensor which detects the position,speed and/or acceleration of the actuator and/or the pressure acting onthe actuator or the forces exerted by the actuator. In this way it ispossible to adapt the drive in a highly variable manner to the actualcircumstances.

With the abovementioned advantageous embodiments it is also possible, ofcourse, to use more than two pumps for driving several actuators.

Further embodiments can be noted from the other sub-claims. In thefollowing the invention will be explained in greater detail withreference to the drawing, wherein:

FIG. 1 shows a basic circuit diagram of the drive;

FIG. 2 shows a basic circuit diagram of a drive system with severalactuators;

FIG. 3 illustrates a second exemplified embodiment of a drive systemwith several actuators, and

FIG. 4 illustrates a third drive system with several actuators.

In the following it is assumed that the drive co-operates with adouble-acting piston arrangement. However, it can in general be combinedwith any hydraulic actuators, for example also with single-actingactuators, hydraulic motors or gear arrangements.

FIG. 1 shows an actuator 1 in the form of a hydraulic double-actingpiston arrangement, which has a piston 5 moving in a cylinder 3, apiston rod 7 being attached to the piston 5. The piston 5 and piston rod7 are positioned in the cylinder 3 in such a way that two pressurechambers 9 and 11 are formed.

The first pressure chamber 9 is connected by a feed line 13 to a pump15, which has a drive assembly 17. This comprises in this case anelectric motor 19, which by way of a shaft 21, which is only indicatedhere, is connected to the first pump 15. The first pump 15 is connectedby a supply line 23 to a tank 25. Parallel to the pump 15 a valve 27 isprovided, which on the one side is connected to the supply line 13 andon the other side to the supply line 23. The valve 27 is in this case anon-return valve which is arranged in such a way that, in the event ofan under-pressure in the supply line 13, the hydraulic medium present inthe tank 25 can be sucked up, also when the first pump 15 is not driven.

Connected to the supply line 13 is an over-pressure valve 29, alsocalled a relief valve, which via a return line 31 is connected to thetank 25. An in this case identically constructed supply system isprovided for the second pressure chamber 11: Via a supply line 13′ asecond pump 15′ conveys a hydraulic medium from the tank 25. To this endthe second pump 15′ is connected via a supply line 23′ to the tank 25.The second pump 15′ is provided with a drive assembly 17′. It ispossible to drive both pumps 15 and 15′ by one single motor, for examplethe electric motor 19. With the exemplified embodiment illustrated here,the drive assembly 17′ comprises a second electric motor 19′, which viaa shaft 21′ indicated here drives the second pump 15′. Parallel to thesecond pump 15′, a valve is again provided here, which is in the form ofa non-return valve 27′ and is arranged in such a way that in the eventof an under-pressure in the supply line 13′ hydraulic medium can besucked up via the supply line 23′ from the tank 25. The supply line 13′is connected via an over-pressure valve 29′ to the return line 31 whichleads to the tank 25.

The hydraulic system associated with the actuator 1 may be provided witha cooler 33, which here is integrated in the supply line 23 to the firstpump 15. It is also possible to install this cooler 33 at any point inthe hydraulic system. Finally, it would also be possible to provide oneor several of the supply lines with cooling ribs to eliminate excessheat.

When via the first pump 15 hydraulic medium is conveyed from the tank 25into the first pressure chamber 9, the piston 5 moves to the rightinside the cylinder 3. As a result also the piston rod 7 is moved to theright. Due to the movement of the piston 5, the pressure in the secondpressure chamber 11 increases. As a result thereof the hydraulic mediumpresent in the pressure chamber 11 is forced back via the supply line13′ to the second pump 15′. The second pump 15′ is now operated as amotor which drives the coupled electric motor 19. The latter now worksas a generator and converts the drive energy into electric energy andfeeds this back into the electric system of the drive, where it can beused again to feed the first electric motor 19. Depending on thedirection of movement of the piston 5, one of the pumps 15, 15′ acts asmotor and the associated electric motor 19, 19′ as generator, whichimproves the efficiency of the drive considerably.

A movement of the piston 5 and piston rod 7 in the opposite directionoccurs when a hydraulic medium or hydraulic oil is supplied by thesecond pump 15′ to the second pressure chamber 11. The to and fromovement of the piston rod 7 is indicated in the Figure by a doublearrow.

The drive for the actuator 1 illustrated in FIG. 1 in addition comprisesa control 35 which via control lines 37 and 37′ is connected to theelectric motors 19 and 19′.

The actuator 1 is associated with at least one sensor 39, the outputsignals of which are fed via a signal line 41 to an evaluation circuit43, which together with the control 35 forms a regulating circuit 45.Via a line 47 at least one external signal can be fed to the evaluationcircuit 43, by means of which the drive for the actuator 1 can beinfluenced.

The sensor 39, which may comprise an analogue/digital converter, is ableto detect the most varying physical parameters of the actuator 1, forexample its position, the speed and/or acceleration of the piston 5 orpiston rod 7, respectively, the pressure prevailing in the supply lines13 and/or 13′ and/or the forces exerted by the actuator 1. It is alsopossible for physical parameters of the actuator 1 to be determinedindirectly by sensors in the supply lines 13 and 13′, respectively, inthe control 35 and/or the evaluation circuit 43 or the electric motors19 and 19′. One or several sensors, for example flow or speed sensors,can also be integrated in the control 35 or in the electric motors 19and 19′. In that case the external sensor 39 may optionally be omittedand a modular construction of the drive can be realised.

FIG. 1 shows that in total one drive can be realised for an actuator 1which permits a two- or four-quadrant operation. This is possible bothwhen the control 35 is provided in the form of a control circuit orwhen, as illustrated in the Figure, it is a regulating circuit, forexample a single-loop regulating circuit. The regulating circuit maycomprise continuous regulators, for example PID and/or conditionregulators with/without observers or discontinuous regulators. It mayalso be constructed in such a way that one or several of the physicalparameters are regulated in parallel or sequentially. To excludepermanent regulating errors of the regulating circuit or regulatingsystem, preferably regulators with integrated parts are used, i.e.regulators with I-, PI- or PID-behaviour. The regulating circuit can berealised by means of the analogue or digital technique or by acombination of analogue and digital techniques.

In FIG. 1 the pumps 15 and 15′ are provided as fixed-displacement pumps,which means that they have a constant displacement volume. It is alsopossible that one or both the pumps are variable displacement pumps, inwhich case one or two displacement chambers can be provided. What isimportant is that also a four-quadrant drive can be realised withoutproviding any throttle valves in the feed lines 13 and 13′. As a resultthe drive for the actuator 1 operates in a particularly low-loss manner.From the above it is also clear that the drive can be realised verysimply and accordingly economically, seeing that also for afour-quadrant drive only pumps with a constant displacement volume arerequired, i.e. pumps that can be realised relatively economically. Onlyone drive is required for the pumps, which permits variable deliveries.This is possible already with the aid of one single electric motor whichhas a variable speed and is controlled by way of the control 35. Thedrive for the actuator 1 can, therefore, be simplified even furthercompared to the illustration in the Figure, in which case nevertheless afour-quadrant drive can be realised.

The drive illustrated here also meets high safety requirements seeingthat on the one hand over-pressure valves 29, 29′ are provided and onthe other hand valves 27, 27′ in the form of after-suction valves. Thevalves 27, 27′, 29 and 29′ have exclusively a safety function and arenot required for the normal operation of the drive, i.e. they areinactive.

A particularly simple design can be achieved in that the electric motors19 and 19′ with the associated pumps 15 and 15′ can be constructed as aunit. The delivery of the pumps is obtained by adapting the motor speedor the number of revolutions, which is possible with the aid of thecontrol 35. The latter can, in addition, be integrated in the unitconsisting of motor and pump, resulting in a particularly compactconstruction. Seeing that the actuator is clamped between the two pumps15 and 15′, a high rigidity is ensured.

From the illustration it can be noted that the areas of the piston 5which are acted upon by the pressure prevailing in the pressure chambers9 and 11, have different sizes. In the first pressure chamber 9, becauseof the piston rod 7, there is an annular area which is smaller than thecross-sectional area of the piston 5 which is acted upon by the pressureprevailing in the second pressure chamber 11. For example, the sizeratio or area ratio of the piston areas acted upon by pressure may be2:1. To compensate for this, the delivery volumes of the pumps 15 and15′ can be adapted to this area ratio. As a result thereof the electricmotors 19 and 19′ can again be operated at the same speed. However, itis obvious that also pumps with the same delivery volume can be usedwhich are operated at different drive speeds.

By using the sensor 39 the simple drive for the actuator can be designedfor a position and pressure regulation and/or for a speed and pressureregulation.

When for at least one of the pumps 15, 15′ a variable displacement pumpis used, the drive for the actuator can, in addition, besides thespeed-dependent delivery regulation by the electric motors 19 and 19′respectively, also be controlled by changing the displacement volume ofthe pumps. It is clear, therefore, that the drive for the actuator 1 canbe changed in many ways and can be adapted to different applications.

In FIG. 2 a drive system 51 is illustrated, which consists of several,in the present case four actuators 1.1 to 1.4. Such a drive system 51 ispart of a machine which performs different operating movements in acompletely or partially sequential manner.

Each of the actuators 1.1 to 1.3 is a hydraulic double-acting pistoncylinder, as already described in connection with FIG. 1. For thatreason they will not be described again. Only the actuator 1,4 isdifferent insofar as this is a hydraulic motor.

The same as with the actuator 1 described in FIG. 1, each of the fouractuators 1.1 to 1.4 is supplied, via feed lines 13 and 13′, with ahydraulic fluid which is delivered by a pump unit 53, surrounded by abroken line, from a tank 25. The same as with the exemplified embodimentof FIG. 1, the pump unit 53 has two pumps 15, 15′, which are driven withthe shaft 21 and 21′, respectively, by the electric motor 19 and 19′,respectively. The two feed lines 23, 23′ of the two pumps 15, 15′ areconnected to the tank 25.

For the sake of clarity, the non-return valves 27, 27′, as well as theover-pressure valves 29, 29′, illustrated in FIG. 1, are shown here as aswitch block 55. However, the mode of functioning is the same as that ofthe valves 27 and 29.

Also for the sake of clarity, a regulating and control unit 57 is shownsimply as a function block. The regulating unit 57 comprises for eachactuator a regulating circuit 45, which includes a control 35 and anevaluation circuit 43. The evaluation circuit 43 associated with anactuator receives the signal supplied by the sensor 39 via the line 41.The connection between the abovementioned components is the same as thatdescribed with reference to FIG. 1, so that at this point no furtherdetails will be given of the exact mode of functioning.

FIG. 2 furthermore shows a valve arrangement 59 which is provided in thefeed lines 13 coming from the two pumps 15, 15′ and leading to theactuators. The valve arrangement has two hydraulic inlets 61.1 and 61.2,the first inlet 61.1 being connected to the pump 15 and the second inlet61.2 to the pump 15′. In addition to these two inlets, for everyactuator 1.1 to 1.4 two outlet 63.1, 63.1′ to 63.4, 63.4′ are provided.The outlets 63.1 to 63.4 are each connected to the feed line 13 of anactuator 1.1 to 1.4, whereas the outlets 63.1′ to 63.4′ are eachconnected to the feed line 13′ of an actuator.

The valve arrangement 59 comprises several, in the present exemplifiedembodiment preferably four switching positions, in which the inlets 61.1and 61.2 are connected in a low-loss manner to predetermined outlets 63.

In the switching position of the valve arrangement 59 illustrated inFIG. 2, the inlet 61.1 is connected to the outlet 63.1 and the inlet61.2 to the outlet 63.1′. As a result the pump 15 is connected to thefeed line 13 and the pump 15′ to the feed line 13′. The mode offunctioning of the actuator 1.1 in co-operation with the regulatingdevice 57 and the pump unit 53 corresponds to the mode of functioning ofthe arrangement in FIG. 1, for which reason another description will bedispensed with at this point.

The switching position of the valve arrangement 59 can be changed, forexample, via a control line 63 by the regulating unit 57. In the presentexemplified embodiment the pump unit 53 is connected in the switchingposition II to the actuator 1.2, in the switching position III to theactuator 1.3 and in a switching position IV to the hydraulic motor 1.4.Naturally, also other associations of the pump unit 53 and the actuatorsper switching position are possible.

FIG. 3 shows an exemplified embodiment which corresponds substantiallyto the aforementioned exemplified embodiment according to FIG. 2. Forthis reason another description of the parts marked with the samereference numerals will be dispensed with. The only difference is thatthe valve arrangement 59 permits a different association of the inlets61.1 and 61,2 with the outlets 63.1 to 63.4.

Thus, in the illustrated switching position of the valve arrangement 59the inlet 61.1 is connected to the outlet 63.2 and the inlet 61.2 to theoutlet 63.4. In addition the valve arrangement 59 has an outlet 65,which via a line 67 leads to the tank 25. This outlet 65 is connected onthe one side to the outlet 63.2′ and on the other side to the outlet63.4′. With the aid of these connections it is possible to use the pump15 for driving the actuator 1.2 and the pump 15′ for driving thehydraulic motor 1.4. By using reversible pumps 15, 15′, it isfurthermore possible to bring about a movement of the actuators in bothdirections.

Depending on the application, the valve arrangement 59 can beconstructed in such a way that a switching position is provided forevery desired operation combination of two actuators.

In FIG. 4 another exemplified embodiment is illustrated, the basicconstruction of which corresponds to the exemplified embodiment shown inFIG. 2. For this reason another description of the parts marked with thesame reference numerals will be dispensed with here.

In the present exemplified embodiment, with the aid of the valvearrangement 59 another mode of operation is made possible. By connectingthe two inlets 61.1, 61.2 to one outlet 63, the two pumps 15, 15′ can beswitched in parallel to supply one actuator 1.

FIG. 4 shows that in the illustrated switching position of the valvearrangement 59 the inlets 61.1 and 61.2 are connected to the outlet 63,whereas the outlet 63.3′ is connected to the outlet 65. As a resultthereof both pumps 15, 15′ supply hydraulic fluid via the feed line 13to the actuator 1.3 for its actuation. In the other switching positionsof the valve arrangement 59 the actuators 1.1, 1.2 and 1.4 can then beconnected to the two pumps 15, 15′.

Naturally, the connections of the pumps 15, 15′ to the feed lines 13,13′ of the individual actuators illustrated in FIGS. 2 to 4 can becombined at will by a suitable construction of the valve arrangement 59.Thus, it is entirely possible in a switching position I to operate theactuator 1.1 in accordance with FIG. 2, in the switching position II touse both pumps for driving the actuators 1.2 and 1.4 and in a switchingposition III to supply the actuator 1.3 via both pumps 15, 15′ inaccordance with FIG. 4.

Furthermore, it is also conceivable to provide a further pump unit inaddition to the pump unit 53 illustrated in the exemplified embodiment,so that several actuators can be operated.

What is claimed is:
 1. A drive system comprising: at least two hydraulicactuators; a first pump and at least one further pump that areconfigured to supply hydraulic fluid to the actuators, wherein the pumpsare bi-directionally speed-regulated; and a valve arrangement having oneinlet for each pump and a number of outlets connected to the actuators,wherein each of the inlets is connected to a pump and wherein the inletsare connected to the outlets in a pre-determined manner; wherein, in afirst switching position of the valve arrangement, a first inlet of thevalve arrangement is connected to a first outlet of the valvearrangement and a second inlet of the valve arrangement is connected toa second outlet of the valve arrangement, wherein the first and secondoutlets are connected to the same actuator.
 2. The drive system asrecited in claim 1, wherein the valve arrangement is switchable betweenthe first switching position and a second switching position, wherein,in the second switching position, the first and second inlets of thevalve arrangement are connected to one outlet of the valve arrangementsuch that both pumps jointly supply one actuator.
 3. The drive system asrecited in claim 1, wherein the valve arrangement is switchable betweenthe first switching position and a second switching position, wherein,in the second switching position, the two pumps are connected todifferent actuators.
 4. The drive system as recited in claim 1, whereinat least one of said pumps has a fixed displacement volume.
 5. The drivesystem as recited in claim 1, wherein at least one of said pumpscomprises a variable displacement pump.
 6. A drive system comprising: atleast two hydraulic actuators; a first pump and at least one furtherpump which are configured to supply hydraulic fluid to the actuators,wherein the pumps are bi-directionally speed-regulated; and a valvearrangement having one inlet for each pump and a number of outletsconnected to the actuators, wherein each of the inlets is connected to apump and wherein the inlets are connected to the outlets in apre-determined manner; wherein, in a first switching position of thevalve arrangement, the two pumps are connected to different actuators;wherein the valve arrangement is switchable between the first switchingposition and a second switching position; and wherein in the secondswitching position, both pumps are connected jointly to one outlet, inorder to supply one actuator.
 7. The drive system as recited in claim 6,wherein at least one of said pumps comprises a variable displacementpump.
 8. The drive system as recited in claim 6, wherein each of the twopumps has a separate drive assembly.
 9. The drive system as recited inclaim 8, further comprising a control circuit configured to control thedrive assemblies.
 10. The drive system as recited in claim 9, whereinthe control circuit comprises at least one sensor adapted to detect aparameter of at least one actuator.
 11. The drive system as recited inclaim 6, further comprising: a regulating circuit configured to controlat least one parameter of at least one actuator.
 12. The drive system asrecited in claim 6, further comprising: at least one electric motoradapted to drive at least one of the pumps, the electric motor havingvariable speed for each direction of rotation.
 13. A drive systemcomprising: at least two hydraulic actuators; a first pump and at leastone further pump which are configured to supply hydraulic fluid to theactuators, wherein the pumps are bi-directionally speed-regulated; and avalve arrangement having one inlet for each pump and a number of outletsconnected to the actuators, wherein each of the inlets is connected to apump and wherein the inlets are connected to the outlets in apre-determined manner; wherein each of the pumps is associated with aseparate electric motor adapted to drive the pump, each electric motorhaving a variable speed for each direction of rotation; wherein thevalve arrangement is switchable between a first switching position and asecond switching position; wherein, in the first switching position ofthe valve arrangement, the two pumps are connected to differentactuators, and in the second switching position of the valvearrangement, both pumps are connected jointly to one outlet, in order tosupply one actuator.
 14. The drive system as recited in claim 13,wherein at least one of said pumps comprises a variable displacementpump.
 15. The drive system as recited in claim 13, further comprising atleast one control circuit configured to control the electric motors. 16.The drive system as recited in claim 15, wherein the control circuitcomprises at least one sensor adapted to detect a parameter of at leastone actuator.
 17. The drive system as recited in claim 13, furthercomprising: a regulating circuit configured to control at least oneparameter of at least one actuator.